Ensure native implementations of getElementsByClassName and compareDocumentPosition. Fixes gh-228.

Also pass all tests with bypass optimizations on by including testinit in the iframe.
Update npm development dependencies; add load-grunt-tasks
Run `grunt build` to avoid testing errors when all you want is the build. Close gh-230.
Clarify some README headers. Supplements gh-230.
No ticket: Small optimization in "text" pseudo. Close gh-227.